I got my 2015 Lux in April 2015. At the time, my 3 girls were ages 6, 5, and 5. For any new seat purchase, I recommend the Diono Radian RXT. You will will fit 3-across the second row with room to spare. In fact, I had two Britax Frontier 85 (convertible to high-back booster) which had an integrated cup-holder on each side and a Radian RXT in the middle and they still fit. There should be numerous posts you can search for if you want more info. The two outboard seats have LATCH anchors and you will need to secure the middle seat with the metal buckle-lock-thing. It's a giant PITA to install, so don't unbuckle this unless you have to. Once you have all seats installed, there is no easy way to get into the third row...best bet is lower suspension to "access" height and have the passenger(s) climb in through the rear. I always thought it was fine for occasional use.
I have had zero issues with engine and transmission. I have found people accustomed to the V8 generally consider it to be superior to the SCV6, but since you have never had one, you would be fine with the V6, which is the same situation I was in. Power is really good when you step on it...but it is a 5,800 lb vehicle and it acts as such.
I am in Northern NJ and honestly, the weakest link I have found with the vehicle (entire brand, really) is the dealer network. Your desired spend seems a tad low for the mileage, especially if you are looking for a CPO with warranty, but it's worth performing a good search. Agree with PaulLR3 on tires, brakes, safety, etc.
For what it's worth, I was on the fence for a while and finally leased my LR4 to give me an "easy out" and I will be purchasing it once it is up. It has been everything I wanted and need in a vehicle and even though you may never go off road, the roads in your area are bad enough that you will be very happy with the ride the air suspension affords.
Best of luck...
